The subject matter disclosed herein relates to elevator systems driven by coated steel belts. More specifically, the subject disclosure relates sheave configurations from elevator systems driven by coated steel belts.
Elevator systems utilize coated steel belts operably connected to an elevator car, and driven by a motor to propel the elevator car along a hoistway. Coated steel belts in particular include a plurality of wires located at least partially within a jacket material. The plurality of wires is often arranged into one or more strands and the strands are then arranged into one or more cords. In an exemplary belt construction, a plurality of cords is typically arranged equally spaced within a jacket in a longitudinal direction.
The motor drives a sheave, in this case a traction sheave, over which the coated steel belt is routed. The belt gains traction at the traction sheave, such that rotation of the traction sheave consequently drives movement of the elevator car. A typical sheave includes a spherical crown on its drive surface to aid the belt in tracking toward a center of the sheave, even when the belt is slightly misaligned. The crown, however, tends to degrade performance of the belt by creating nonuniform contact pressure between the belt and sheave along a width of the sheave. Contact pressure peaks at the center of the belt, resulting in reduced life of the belt relative to a belt subjected to uniform contact pressure.
In addition, because of the high stiffness of the cords, the cords all tend to move at the same speed. The speed of the sheave surface, on the other hand, is directly proportional to a distance between a sheave centerline and an outer surface of the sheave. Because of the crown, the center of the sheave travels at a higher circumferential speed than either end of the sheave. Thus, there are locations along the sheave where the sheave rotational speed will vary from the belt speed, resulting in localized slipping of the belt relative to the sheave, resulting in belt wear.